The present invention relates to the joining of fabrics made of advanced fibers for making pre-forms for composite materials.
More particularly, the invention provides a sewing machine needle which can be used to join fabrics by stitching with a brittle thread.
In the present specification, as in other prior documents, the terms “sewing thread” “brittle thread” “brittle fiber thread” “advanced fiber thread” “high performance threads” “technical fiber” are used interchangeably to designate a thread made from glass, ceramic, graphite or carbon fibers of a commercially or experimentally available type. No novelty is claimed here regarding the thread.
Composite fiber-reinforced materials are widely used wherever a high strength/weight ratio is needed, for example in aerospace vehicles and sports equipment. Glass and carbon fibers have long been used for reinforcing other materials, particularly plastics, in order to improve stiffness and tensile strength. The most popular method of manufacturing composite material is by laminating layers of advanced fibrous material and impregnating the layers with a resin. Such structure is vulnerable to delamination since the strength of the bonding between the layers is limited to the strength of the matrix. Ideally, the layers should be stitched together with the same fibrous material that they are made of in order to increase the interlayer strength and to prevent delamination of the material. Stitching with advanced fibrous yarn is difficult since such fibers are brittle and sensitive to sharp bending and friction.
Threads based on carbon or glass fibers are commercially available. It has however been found that when sharply bent or when friction is applied, such yarns tend to break. The standard sewing machines apply very sharp bends to the threads as well as friction with the sewing needle eye during the sewing process. Hence, they are inadequate for stitching with brittle yarns.
The key component of a stitching device is the sewing machine needle which pierces the fabrics being joined, carries a thread loop through the material, and retracts while leaving the loop protruding or hooked to the other side of the fabrics. The fabrics being joined are moved and the stitching procedure is repeated at an adjacent site. The loops can be engaged by a second lower thread, as is seen in common sewing machines, or other methods.
The state of the art can be assessed from a brief review of recent U.S. Patents.
Takei et al. show a machine needle in U.S. Pat. No. 5,392,725, claiming improved clearance between the blade of the needle and the thread. However the text refers mainly to needle manufacturing methods.
Cahuzac in U.S. Pat. No. 5,515,798 claims a stitching head and needle guide, the needle 33 seen is substantially of conventional design.
Baxter discloses a blind stitching apparatus featuring a curved needle as seen in U.S. Pat. No. 5,829,373. The stitches are placed at discrete-locations to join pre-forms to make a composite component.
A sewing machine needle having offset eye webs is claimed by Vornholt in U.S. Pat. No. 6,318,280. The needle eye is bordered by off-set spaced eye webs. In U.S. Pat. No. 6,332,417 the same inventor details a further needle having a slender eye.
A similar needle is disclosed by Wohnhas et al, in U.S. Pat. No. 6,332,416. Improved loop formation is claimed, due to a protuberance adjoining the eye outlet.